Update some dependencies
Add alembic and new `indico` cli script
Fix setting deletion
Make shell context a bit nicer
Update SQLalchemy

Note: sqlalchemy 0.9.4+ currently breaks Location.getBuildings()
Add `indico db prepare` command to init a new db
Move dev server to `indico runserver`

Also remove `indico_shell` which is now superseded by `indico`
Mention nullable/default quirk when adding columns